Cathode



'March 16, 1.943. R B AYER 2,314,065

CATHODE Filed March 7, 1942 INVENTOR Raymond B. A l/er B am - ATTEIRNEYPatented Mar. 16, 1943 CATHODE Raymond B. Ayer, Verona, N. J .,Vassigner to Radio Corporationof America, a corporation of DelawareApplication March 7, 1942', Serial No. 433,750

(Cl. Z50-27.5)

Claims.

My invention relates to electron discharge devices of the transmitter orpower type, particularly to fllamentary cathodes for such devices.

Filamentary cathodes in transmitter or power tubes designed for singlephase power supply are limited in length and in operating voltage. Longslender filaments are diilicult to support, braces of insulatingceramics and the like which contact the filament deteriorate and crumbleat operating temperatures, and high operating voltages for the lamentcause hum in the tube output. There are practical limits to the currentrating and cross sectional area of the filament because of themechanical difficulties in shaping heavy filaments from the brittlerefractory metals, such as tungsten, and because of the increased costof high current-low voltage power supply equipment.

An object of my invention is a fllamentary cathode for transmitter orpower tubes in which the voltage as well as the current for high cathodepower is moderate.

Another object of my invention is a fllamentary cathode for power tubes,which has moderate current requirements, low voltages between filamentlead-in conductors, which produces negligible hum in the tube output,which is rugged in construction, and which is easy to manufacture.

The characteristic features of my invention are defined in the appendedclaims and one embodiment thereof is described in the followingspecification and shown in the accompanying drawing in which Figure 1shows a longitudinal section of a fluid-cooled transmitting tube havingmy improved fllamentary cathode, Figure 2 is an elevational View of theoperative portion of my improved cathode, Figure 3 is an end View of thecathode of Figure 2, and Figure 4 is a wiring diagram of the filamentcoils of my improved cathode.

One electron discharge device in which my improved cathode isparticularly useful comprises an envelope with a conventionalfluid-cooled anode I sealed at its upper end to a glass bulb 2, throughwhich the grid and iilament lead-in conductor may be sealed. T'he grid 3may be wound on side rods and supported on a clamp around the reentrantstem at the outer end of the bulb. The usual heat and electron shieldsll and 5 may be placed across the end of the anode to protect the glassportions of the envelope.

The cathode 6 comprises, according to my invention, a plurality ofend-to-end coaxial helices or spirals 1, 8 and 9 of coiled wiresupported, in the particular illustrated embodiment, on three parallelspaced filament support rods and current conductors I, I I and I2. Eachsupport rod is mechanically supported in the glass bulb and isexternally connected to current supply terminals. The end of each coilis bent out of the cylindrical surface of the coil and is attached, asby binding or welding, to one of the support rods. The opposite ends ofeach coil is attached to a different rod, the connections being made sothat'the lilament presents a polyphase loadlto cathode terminals of thetube. The particular coil connections shown are of the delta type andare diagrammatically as shown in Figurel. By making the ohmic resistanceof the coils equal, a-balanced three-phase power supply may be appliedto the three-filament terminals and the cathode operated with negligiblehum disturbance.

A lament, with a given current and power rating, has, when constructedaccording to my invention, an operating voltage of only 57.6% of theoperating voltage of a corresponding filament made in the usual way withsingle phase connections. Further, my improved filament with threedistinct coils, supported at six points, is to be distinguished from acorresponding filament with a single coil for single phase powersupported only at two widely spaced points. The increased rigidity of mylament is of particular importance in tubes that must withstand roughhandling and vibration in use.

My improved filament is particularly adapted for power tubes of the typeshown in the Zottu et al. Patent 2,228,939, January 14, 1941, where thetotal lament power is of the order of 7.0 kilowatts, where the operativelength of the filament is '7 inches, and Where its diameter is 1 inch.Tungsten or thoriated tungsten wire may be used.

Should increased rigidity of the coils be desired, each coil, 1, 8 and9, may be divided into sections of uniform length and the sectionsconnected to corresponding pairs of support rods and operated inelectrical parallel. Further, the iilament may be arranged to operatewith polyphased power with any desired number of phases. The coils maybe supported on and connected to three support rods for three-phaseoperation as shown, or for quarter-phase operation. Six-phase operation,for example, may be obtained with six rods and six coils. Should star orY polyphase connections be desired, the number of support rods must, ofcourse, exceed by one the number of phases used. Should single phaseoperation be desired, the corresponding ends of the several coils wouldbe connected to a common support rod or to different support rodselectrically connected in parallel.

The support rods I0, Il and l2 are preferably disposed along the insideof `the illament coils and the ends of the coils bent inwardly andattached to the rods as shown, but if desired the rods may be disposedoutside the coils, where the spacing between the cathode and gridpermits.

My improved lament is adapted for transmitter or power tubes, is notlimited in its overall length and may be operated for a given power atmoderate voltages. My improved filament produces a minimum of humdisturbance in the output of its tube, is rugged in construction and iseasy to manufacture.

I claim:

1. A filamentary cathode comprising a plurality of coaxial helices,support rods for said helices arranged longitudinally of the helices,the end of each helix being bent from the surface of its cylindricalsurface and attached to one of the rods, the electrical connections tothe rods being arranged so that the electrical resistance through thehelices between any pair of rods is uniform.

2. A polyphase cathode comprising a plurality of coaxial coils, aplurality of parallel spaced metal current conducting support rodsdisposed lengthwise of said coils, the ends of said coils beingmechanically attached to said rods, the electrical connections of thecoils to the rods being arranged to present a balanced polyphaseelectrical load to the rod terminals.

3. A cathode for power tubes comprising a plurality of end-to-endhelices of electron emissive wire, a plurality of parallel support rods,the rods being disposed lengthwise of the helices and in spaced relationto the surface of the helices, the ends of the helices beingmechanically and electrically attached to said rods.

4. A three-phase cathode comprising three end-to-end coaxial helices,three spaced parallel metal support rods in and disposed lengthwise ofthe helices, the opposite ends of each helix being connected to adifferent pair of said rods to provide a balanced uniform electricalload between each of said pairs of rods.

5. An electron discharge device comprising a tubular anode and acathode, said cathode comprising an electron emissive filament spiralledin a substantially cylindrical surface and disposed substantiallycoaxial with said anode, and means to supply current to a plurality ofpoints on said lament intermediate its ends and to rigidly support saidfilament in xed spaced relation with said anode, said means comprising aplurality of spaced metal rods supported at one end of the electrondischarge device and extending in parallel relation to the opposite endof the device, the filament wires being bent out of said cylindricalsurface at a plurality of intermediate points along the length of thecathode, and connected to said rods.

RAYMOND B. AYER.

